This one is a strange one in that Peter Lorre and Sydney Greenstreet, instead of hounding Humphrey Bogart, actually team up to find out what happened to an evil criminal. Lorre actually plays the hero of sorts to the film as a mystery writer who, due to curiosity, starts trying to find out more of the criminal after seeing the man's apparent corpse. The reason I only say this is a decent enough mystery actually is that there is not enough of Lorre's search for the truth and too much of the flashbacks that show what Dimitrios was doing before the start of the film. Those scenes frankly just aren't that interesting particularly, and it is not helped by the fact neither Lorre nor Greenstreet appear in them.
Lorre's role here is rather strange one in that the writer Cornelius is always an observer of the events and only really gets involved directly with the turn of events at the very end of the film when he has to fight for his life. Before that point Cornelius goes along from place to place checking out various clues while being somewhat perplexed by Greenstreet's character who is a man who clearly knows more then he says as well seems to go by many names. Lorre's role is quite simplistic in nature and in terms of conception the story of Dimitrious should be far more interesting but it is a strong testament to Lorre's talent that he steals the film anyway.
It's funny that Lorre played so many villains so well because he is able to be such a charming fellow with such an innate likability. Lorre is just fun to be around with in this film and things are only helped once Sydney Greenstreet shows up. It is no surprise that Greenstreet and Lorre were in so many films together as they just have some great chemistry together. The two are quite brilliant at making the dialogue sing especially well giving their scenes together a wonderful life to them something that is sorely missing from the scenes without them. Lorre and Greenstreet are just terrific to watch to see them go along through the plot where they are able to bring the humor almost just through the style of their back and fourths.
Honestly this is not really much of a role in any way shape or form. Cornelius doesn't really have a back story, his motivation for getting involved in the plot is fairly weak, and he really doesn't have very much even to do. None of that matters though because Peter Lorre is in the role and that is apparently all it takes for the role to be rather interesting. Peter Lorre is incredibly enjoyable to be around so to speak and he makes it fun to go through the plot of the film with him. It is unfortunate that the part has absolutely no meat to it and would be just one big nothing if it were not for Lorre. This is not a great performance by Peter Lorre but it is a great example of a great actor doing something with almost nothing.